1. Field of the Invention
The present invention relates to a semiconductor device composed of complementary field effect transistors (MOSFETs) with increased carrier mobilities of both polarities by applying orientation-dependent mechanical stresses to their respective semiconductor channel regions and a method of manufacturing thereof.
2. Description of the Related Art
Recently, in order to increase the operation speed of MOSFETs, a method of enhancing mobilities of carriers (i.e., electrons or holes) by applying mechanical stresses to the channel-forming semiconductor portions and thereby modulating the electronic states of the conduction band and the valence band of the semiconductor has been proposed (H. Irie et al. IEDM Tech. Dig. pp. 225-228, 2004).
In order to produce such mechanical stresses in the channel regions, one can deposit an additional stress-yielding insulator film, having high internal stress, over the MOSFETs after their formation. With this method, however, most of the stress from the stress-yielding insulator would come to be applied to the gate electrodes, not to the channel regions. Thus, this method greatly suffers from its inefficiency in stress generation within the channel.
Such dissipation of stresses can be avoided by replacing a portion of each of the source and drain regions with a foreign stress-generating semiconductor substance with high internal stress other than the channel forming semiconductor (Si) (T. Ghani et al., IEDM Tech. Dig. pp. 978-980, 2003).
Compressive stress in the channel direction increases the hole mobility, whereas, tensile stress applied in the channel direction increases the electron mobility (H. Irie et al., IEDM Tech. Dig. pp. 225-228, 2004).
Thus, in order to realize a high-speed p-type MOSFET (p-MOSFET), indispensable to manufacturing of advanced complementary MOSFETs (C-MOSFETs) circuits, a portion of each of its source and drain regions must be replaced by an expansive semiconductor substance with a larger-than-silicon lattice constant (for example, a eutectic of silicon and germanium (SiGe)). Likewise, a contractile semiconductor material with a smaller-than-silicon lattice constant (for example, a eutectic of silicon and carbon (SiC)) needs to be epitaxially formed in portions of the source and drain regions to increase the speed of the n-type MOSFET (n-MOSFET).
For C-MOSFETs manufacturing, therefore, two extrinsic semiconductor materials with incompatible lattice constants have to be placed in close proximity to each other. Of course, during the epitaxial growth of one of the semiconductor materials, the adjacent region to form the other semiconductor material must be coated with an insulating layer to prevent unwanted growth of the first material. Accordingly, the completion of the C-MOSFETs naturally requires repeated steps of insulating layer deposition and extremely precise lithography as well as etching and patterning of fine structures of the insulating layer.
Besides, it is, in itself, difficult to epitaxially grow an uniform heterogeneous semiconductor material on the Si substrate in a well-controlled manner. Moreover, this unstable process step must be repeated twice for the two incompatible semiconductor materials, which results in complication of the manufacturing steps and increased manufacturing cost. In addition, an expansive semiconductor material placed in close proximity to a contractile semiconductor material results in substantial cancellation of the individual strains exerted by the semiconductor materials and, therefore, the stresses induced in the respective channels will be greatly reduced.
Furthermore, epitaxial growth of an extrinsic semiconductor material having a different lattice constant from the substrate naturally induces a large number of crystal defects at the hetero-junction between the semiconductors of the incompatible lattice constants. The dense array of the crystal defects in the vicinity of the source/drain junctions inevitably causes severe junction leakage from the source/drain regions to the substrate semiconductor below.